1. Field of the Invention
This invention relates to the packaging of optoelectronic devices. More particularly, the present invention relates to optoelectronic packaging assemblies that provide for optical coupling, cooling, and high-speed electrical operations.
2. Discussion of the Related Art
Despite advances in data- and telecommunications systems, overall system bandwidths remain limited by the need to interconnect various system modules. Decreasing device sizes have not solved fundamental signal flow bottlenecks, the problems have only shifted to package, module, and interconnection levels. Despite rapid improvements in electromagnetic simulation tools and increasing computational power, signal flow issues still requires a designer's full attention and creativity in the research and development phases. More importantly, practical signal flow designs must engage various mechanical, thermal, hermetic, material, and manufacturability concerns to meet cost targets and customer specifications
Signal flow in optoelectronic applications frequently involves analog and/or digital signals together with light radiation through optical fibers. Such applications usually include optoelectronic devices, such as laser diodes, LEDs, photodiodes, and phototransistors that must be coupled with an optical fiber. One significant problem is coupling with the required alignment accuracy and stability over time and temperature. Manually aligning optical components with optical fibers is time consuming and costly.
Because of the extremely high frequencies of the light used in optical systems, such systems can potentially operate with exceptionally wide bandwidths. Unfortunately, the electrical systems required to actually use the available bandwidth are often difficult to implement. For example, most prior art optoelectronic packages when operated at GHz frequencies have excessive dielectric signal losses. Furthermore, electrical signal reflections caused by impedance mismatches at the package can be seriously detrimental to system performance. Additionally, undesired electrical resonance can exist inside an optoelectronic package, resulting in a poor performance.
To prevent excessive dielectric signal losses, optoelectronic packaging should be fabricated from dielectric materials having low dissipation factors. Unfortunately, such materials often have undesirable cost, thermal, and molding characteristics. For example, polytetrafluoroethylene, which has very low dielectric loss, may be too expensive for some application and can be difficult to mold. To reduce line reflections, the optoelectronic package should have carefully controlled input impedances, but this has been very difficult to do, particularly in mass-produced optoelectronic packaging assemblies. Finally, preventing or reducing undesired electrical resonance has been as much black art as solid engineering.
One optoelectronic package assembly that has been successful, at least at relatively low operating frequencies, is the so-called butterfly package 20 illustrated in FIG. 1. As shown, the package 20 includes a body 22 having a cavity 24 defined between walls 25. The body 22 is typically comprised of KOVAR, a bulky, marginally conductive material that requires costly machining. The cavity 24 is dimensioned to receive an optoelectronic component or assembly, which is not shown for clarity. A plurality of pins 26 extends from the body 22. The body 22 further includes a mounting flange 28 having mounting holes 30 for mounting the package 20 to an external structure. The body 22 also includes a fiber input receptacle 32 for receiving an optical fiber. Finally, while not shown for clarity, the optoelectronic packaging assembly 20 beneficially includes a cover for sealing the cavity 24.
The package 20 represents an industry standard package. Among other features, the pins 26 have a standard footprint, and the mounting holes 30 and the receptacle 32 are located and dimensioned according to a predetermined configuration. This enables system designers to efficiently incorporate the package 20 into their designs. Furthermore, the standard footprint and dimensions enable the use of standardized optoelectronic workbenches and assembly machines to mount optoelectronic components or assemblies into the optoelectronic packaging assembly 20, to align an optical fiber with the mounted optoelectronic components or assemblies, and to electrically interconnect the optoelectronic components or assemblies to the pins 26. These general features are beneficially incorporated in mass-produced optoelectronic packaging assemblies.
While the package 20 is generally successful, it suffers from various limitations. First, such optoelectronic packaging assemblies generally have poor heat dissipation characteristics. Second, the walls 25 tend to be relatively high, thus increasing the difficulty of mounting and then electrically and optically interconnecting a contained optoelectronic component or assembly with an optical fiber. Other limitations of the package 20 are its relatively poor control of the impedance of the pins 26, a susceptibility to internal resonance, and signal radiation and/or noise pick-up.
Therefore, an optoelectronic packaging assembly that provides for input/output electrical connections, for easy mounting of an optoelectronic device and its associated components, for relatively simple, accurate and stable optical alignment, and for high speed electrical characteristics would be beneficial.